1. Field of the Invention
The present invention relates to an image processing apparatus and a control method thereof for an image forming apparatus which forms an image by a light emitting unit using a plurality of light emitting elements.
2. Description of the Related Art
In the related art, an electrophotographic image forming apparatus which forms an image using a recording head including a plurality of light emitting elements such as a light emitting diode (LED) is known. The electrophotographic image forming apparatus, generally, forms an image through a plurality of processes such as charging, exposure, development, transferring, fixing, and cleaning.
Here, an image forming process in a general electrophotographic method will be described. First, a charging unit uniformly charges a photosensitive member, which is an image bearing member, and then a light emitting element, which is an exposure unit, exposes the photosensitive member according to an image signal to form an electrostatic latent image on the photosensitive member. Further, a recording head including a light emitting element is disposed to be parallel to a rotational shaft of the photosensitive member. Thereafter, a development unit develops the electrostatic latent image on the photosensitive member and forms a toner image on the photosensitive member. In this case, after the development unit charges toner, the toner is applied to the photosensitive member using a development roller rotating at a substantially constant speed, and the toner is attached onto the electrostatic latent image to form a toner image. In addition, the toner image on the photosensitive member is transferred and fixed onto a recording medium to form an image. Further, transfer residual toner remaining on the photosensitive member is collected by a cleaning unit.
In such an image forming apparatus, deterioration in an image quality such as a streak noise may occur due to deterioration of the light emitting element. Generally, a light emitting efficiency of the light emitting element such as an LED is lowered as the deterioration progresses. Therefore, if a light emitting frequency of a specific light emitting element among a plurality of light emitting elements of the recording head is high, a density of an image region formed by the corresponding light emitting element is lower than the density of an image region formed by other light emitting elements so that the image region formed by the specific light emitting element is considered as a streak noise.
Japanese Patent Application Laid-Open No. 2007-83558 discusses a method in which a lighting amount of the deteriorated light emitting element is increased more than a reference lighting amount to uniformize a variation of a light quantity of an LED head.
Further, Japanese Patent Application Laid-Open No. 4-267276 discusses a method in which input image data corresponding to a light emitting element is shifted in an arrangement direction of the light emitting element to prevent the light emitting frequency from being concentrated on a specific element.
However, according to the method discussed in Japanese Patent Application Laid-Open No. 2007-83558, the streak noise of the image may be suppressed but the deterioration of the light emitting element is sped up.
Further, according to the method discussed in Japanese Patent Application Laid-Open No. 4-267276, even though the variation of a usage amount of the light emitting element is suppressed to uniformize a light emission amount of each of the light emitting elements, the image formed position on a recording medium is deviated. In addition, when an image is formed using a plurality of colors, if the correction is independently performed for each color, registration is deviated. In the meantime, if the same correction is performed for each color, a color of which variation of a usage amount of the light emitting element cannot be suppressed may be generated.